Routing Switching Subnetting

7/28/2019 Routing Switching Subnetting

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ROUTING


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Routing

Routing- process when router receive a packet, analyzethe dest. address info and select the path for the packetand forward to the next router.

Hop- each route that a packet takes to reach the nextdevice is called hop.

Encapsulation- IP header that contains addressinformation and other bits that identify the networklayer PDU.

Decapsulation- Process of removing the Layer 2encapsulation data.

Network protocol- IPv4, IPv6, Novell IPX, AppleTalk,CLNS

Default Gateway- address of a router interface that isconnected to the same network.


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A router takes the following steps:

1) The router first discards the Layer 2encapsulation so that the IP can be examined.

2) The router examined the IP address.

3) The router checks the routing table for a match.

4) If the destination is directly connected network,the packet is forwarded to the interface to whichthe network is connected.

5) If the destination is on remote network, the

router either: Forward the packet to the next-hop

Uses the default route

Drops the packet


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If a route to a destination does not exists, the packetcannot be forwarded.

The route would only indicate the next-hop router towhich packet is to be forwarded, not the final router.

3 main feature in routing table is Destination network

Next-hop Metric

If there are two or more possible route to the samedestination, the lowest metric route will be choose.

Default route- used when the destination network isnot represent by any other route in routing table. (needto be configured)


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2 ways router can learn information

about routesStatic routing Dynamic routing

Route information that can be manually

configured.

Learn about routes automatically

Example: Default route Update arrive from other routers without

administrative configuration

Require network admin to initial set up

and configured for any changes of routes

Has higher router processing overhead

Reliable and does not use much

overhead

Reduce administrative cost

Do not update automatically, hence havehigher continuing administrative costs.

If network structure change, these

changes has to be manually update on

every router.


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IP Routing Protocols

RIP (Routing Information Protocol)

IGRP (Interior Gateway Routing Protocol)

EIGRP (Enhanced Interior Gateway Routing Protocol)

OSPF (Open Shortest Path First)

IS-IS (Intermediate System-to-Intermediate System) BGP (Border Gateway Protocol)


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RIP (Routing Information Protocol)

Distance vector routing protocol.

Use hop count as its only metrics for path

selection.

Advertise routes with hop counts greater than

15 are considered unreachable.

Routing table updates are broadcast every 30seconds.


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RIP Operation

1. Request to all RIP neighbor to sent theircomplete routing table.

2. A response message is sent back by all RIP-enabled neighbor.

3. If the route is new entry, the receiving routerinstalls the route in the routing table.

4. If the route is already in the table, the existingentry will be replaced if the new entry has a

better hop count.5. The router then sends a triggered update out

all RPI-enable interface, so that all RIPneighbors can be informed of any new routes.


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RIP request/response example


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EIGRP(Enhanced Interior Routing

Protocol)

Distance vector routing protocol.

Provide reliable and unreliable delivery of packet. (RTP)

Used bandwidth and delay as a metrics for pathselection.

Diffusing Update Algorithm(DUAL)- to keep the tableupdated and select a route.

Changes in the routing information, such as a new linkor a link become unavailable, cause a routing update to

occur. EIGRPs DUAL maintain a topology table separate from

the routing table, which includes the best path to adestination network and any backup paths.


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1. R2 network goes down, R2 sends an EIGRP updatemessage to its neighbor indicating the network its down.

2. RI and R3 return an EIGRP acknowledgement indicatingthat they have received the update from R2.

3. R2 does not have any backup route. So, R2 sends an EIGRPquery to its neighbors asking them whether they have aroute to this downed network.

4. RI and R3 return an EIGRP acknowledgement indicatingthat they have received the query from R2.

5. R1 and R3 send reply message in response to the query.6. R2 returns an acknowledgement indicating that it received

the reply.

DUAL Introduction


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1. UPDATE 1. UPDATE

Figure 1

2. ACK 2. ACK

Figure 2

3. QUERY 3. QUERY

Figure 3

4. ACK 4.ACK

6. ACK 6. ACK

Figure 4

5. REPLY 5. REPLY


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OSPF(Open Shortest Path First)

Link state and classless routing protocol.

Fast convergence and scalability to much largernetwork implementation.

Hello Protocol- use to establish neighboradjacencies before OSPF router can flood its linkto other router.

By default, OSPF Hello packet are sent every 10seconds.

Dead interval- is the period when the router willwait to received the Hello packet before declaringthe neighbor down.


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Each OSPF router maintains a link-state databasecontaining the LSAs received from all other routers.

Then the router built its local link-state database anduse Dijkstras shortest path first algorithm to create anSPF tree.

The SPF algorithm places each router at the root of thetree and calculates the shortest path to each node.

It is based on the cumulative cost required to reacheach node. The cost is based on bandwidth.

OSPF Algorithm


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SWITCHING


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Switching

Each port of the switch represent a separate

collision domain and provides full media

bandwidth to the nodes that connected on that

port.Throughput increased:

-Dedicated bandwidth to each port

-Collision-free domain

-Full-duplex operation


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Forwarding Based on the MAC Address

Switch maintains a table, called a MAC table, that mapsdestination MAC addresses with the port to connect toeach node.

The destination MAC address is used by the switch to

determine to which port the frame should beforwarded.

For each incoming frame, the destination MAC addressin the header is compared to the list of addresses inthe MAC table.

And if a match found, the port number in the table thatis paired with the MAC address is used as exit port forthe frame.


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ARP(Address Resolution Protocol)

ARP provide 2 basic function:

Resolving IPv4 addresses to MAC addresses

Maintaining a cache of mapping


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Resolving IPv4 addresses to MAC

addresses

When IPv4 packet is sent to the data link layer

to be encapsulate into a frame, the device

must identify the data link layer address(MAC)

that is mapped to the destination IPv4address.

To find the MAC address, the node will refer to

a table in its RAM memory called ARPtable/ARP cache.


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Maintaining a Cache of Mappings

There are two ways that a device can gather MACaddresses. One way is to monitor the traffic that occurs on the

local network segment. As a node receives frames

from the media, it can record the source IP and MACaddress as a mapping in the ARP table.

Another way is Layer 2 broadcast ARP request to alldevices on the Ethernet LAN. The frame contains anARP request packet with the IP address of the

destination host. The node receiving will reply packetback to the sender. This response is then used to makea new entry in the ARP table.


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SUBNETTING


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Network Address Class


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Classless Addressing-Example Method 1

Address given 205.16.37.39/28 What is the first address in the block

11001101 00010000 00100101 00100111

(rightmost 32-n bits to 0s)

11001101 00010000 00100101 00100000

205.16.37.32

What is the last address in the block 11001101 00010000 00100101 00100111

(rightmost 32-n bits to 1s)

11001101 00010000 00100101 00101111

205.16.37.47

Find the number of addresses The value of n is 28, which means that number of addresses is 232-28 or

16


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Classless Addressing-Example Method 2

Address given 205.16.37.39/28

As we know the mask is 255.255.255.240 What is the first address in the block (ANDing the given address with

mask) Address: 11001101 00010000 00100101 00100111

Mask: 11111111 11111111 11111111 11110000

First Address: 11001101 00010000 00100101 00100000

What is the last address in the block (ORing the given address with thecomplement of the mask)

Address: 11001101 00010000 00100101 00100111

Mask comp.: 00000000 00000000 00000000 00001111

Last Address: 11001101 00010000 00100101 00101111

Find the number of addresses (mask comp. change to decimal numberand adding 1)

Mask comp.: 00000000 00000000 00000000 00001111

Number of add.: 15+1 = 16


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Date post:	03-Apr-2018
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Routing Switching Subnetting

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